1. Field of Invention
The present invention relates to semiconductor devices and methods for making the same, and particularly, an electrode structure for connecting an external connecting terminal, such as a bonding wire, to an IC chip and a method for making the same.
2. Description of Related Art
A high density arrangement of electrodes (pads) for connecting external connecting terminals, such as a bonding wire, has been required due to the increasing integration density of ICs.
A cross-sectional view of a bonding pad formed using three layers of wiring is exemplified in FIG. 23.
In a structure as shown in FIG. 23, some problems, such as disconnection due to bumps of aluminum wiring and a narrowed bonding region, often arise.
Specifically, when superposing an aluminum pad 8010 as a first layer, an aluminum pad 8110 as a second layer and an aluminum pad 8310 as a third layer, the thickness of each aluminum layer decreases due to a steep slope between different levels, and disconnection due to bumps will readily occur. There is a fair possibility of disconnection due to bumps at a region surrounded with a chain-line circle 8500 in FIG. 23.
The bonding region decreases with an increased number of electrode layers. As shown in the bottom side of FIG. 23, the end of a region capable of bonding in the first pad layer 8010 is represented by P1, the end of a region capable of bonding in the second pad layer 8110 is represented by P2, the end of a region capable of bonding in the third pad layer 8310 is represented by P3, and thus a bonding region decreases as a new layer is superposed. When further superposition of the electrode layers is accelerated, the first electrode layer therefore must have a large area in order to secure the bonding area, and it is difficult to arrange the bonding pad with high density.